Effect of Chlorpyrifos on Thyroid Gland of Adult Male Albino Rats

Introduction: Chlorpyrifos (CPF) is the most widely used organophosphorus insecticide. Aim of the Work: This work aimed to clarify effects of repeated doses of chlorpyrifos on thyroid gland of adult male albino rats. Materials and Methods: Fifteen adult male rats were used. They were divided into two groups: control and chlorpyrifos treated. On sacrifice, blood samples were drawn to determine serum T3, T4 and TSH levels. Thyroid glands were processed for histological, histochemical, immunohistochemical and morphometrical studies. Results: Chlorpyrifos treated rats showed a highly significant decreased body weight, decreased thyroid weight, decreased T3 and T4 and increased TSH hormone levels. Histologically, there was decrease in the size of follicles and amount of colloid, focal degeneration of follicular cells, thickened collagen fibers and congested blood vessels. Histochemically, there was decrease in the PAS reaction. Immunohistchemically, there was a strong caspase 3 and a weak thyroglobulin protein expressions. Ultrastructurally, treated rats had small heterochromatic nuclei, degenerated mitochondria and few secretory granules. Morphometrically there was a highly significant decreased size of thyroid follicles, decreased area % of colloid and increased area % of collagen fibers. Conclusion: CPF could seriously affect thyroid glands with decreased thyroid hormones which play an important role in most of body physiological processes. Use of CPF and other insecticides should be extremely limited and be under many precautions.